I have two Dell Inspiron 530's. The #1 computer has a DVI connector for the monitor and then it also has a VGA connection but it is covered with a black cap. The #2 computer only has a VGA connection. so I want to hook up two computers to one monitor. I have a KVM switch, and the cables are for a VGA connection. So I bought an adapter so that I could hook up my VGA cable to my DVI card. But when I TURN on the first computer I do not get anything on the screen, I have tried to change the settings from digital to analog on the monitor but that does not WORK, the 2nd computer works fine with the monitor. So my question is why is my monitor not working do I have to change some settings somewhere in order for my computer to recognize the VGA cable? The same black screen appears when I hook up the monitor to the VGA port on computer #1 - (after I REMOVE the cap which has a NO symbol on it). Dell only many a few Inspirons that were desktops; almost all were laptops. So you've got an Inspiron 530 Desktop.

#1 MUST have a separate video card so the ONBOARD video has been turned off in the BIOS. You should be able to make it the "primary", then you would not need the adapter.Check your resolutions and refresh rates to make sure you aren't overdriving the display.
Does the monitor have an option to choose your signal source?
Also, what's the monitors make and model?CRT or LCD? What kind of inputs does the monitor have? Just VGA or is there another choice.